Full of snark with heart, and scads of exploding high school seniors, "Spontaneous" (now on demand, as in "I demand to see the bodies explode") will likely hold some interest for those looking for sardonic, black-comic relief from 2020 pandemic living. 

In this tale, at least, the carnage appears to be unpreventable as well as random. Based on Aaron Starmer's 2016 YA novel, writer-director Brian Duffield's slick adaptation relies on random geysers of death built for startling sight gags.

The story is simple: It's about an unexplained and extremely messy series of combusting seniors, played mostly for laughs and then, at strategic intervals, more seriously, whether or not you buy the seriousness.

Katherine Langford ("13 Reasons Why") glides through as Mara, our wisecracking narrator. Her romance with Dylan, her fellow irony-mainlining outsider played by Charlie Plummer, turns into the main selling point of "Spontaneous." These two make sense together, as characters and as actors. For those who see this film as a worthy successor to "Heathers," or "Carrie," they're the reason why.

The first kid, sitting in pre-calculus class like it's an ordinary day, blows before the 45-second mark. "It was like a Cronenberg movie," Dylan says, referencing "Scanners." Mara likes what she hears: As her longtime best friend Tess (Hayley Law) watches from the sidelines, a romance unfolds in familiar YA-toolkit fashion.

The initial blast leads to frantic images of bloodied students on the run, screaming, evoking another all-American school shooting. But there seems to be no clear adversary or cause underneath the violence in "Spontaneous." It's simply an outlandish manifestation of senior-itis, or adolescent anxieties, or hormones. The feds swoop in and quarantine the surviving students.

"I think this is our life now," one says. "People have been dying for seven months!" says another. A lot of screenplays filmed a year or two ago sound like ancient history now. This one sounds like now — a different, mask-free now.

The name-checking runs rampant along with the students after the latest splurch: "Back to the Future," "E.T.," you name it. If John Hughes ended up with either David Cronenberg or Stephen King as a lab partner, the result would be "Spontaneous." Piper Perabo and Rob Huebel portray Mara's concerned parents, alternating between "tolerant" and "enabling," as they get high with their shaken but guarded daughter, and watch as she struggles to cope with the cumulative emotional and psychological fallout.

And there's the limitation and the problem with a pretty diverting movie. There's something dodgy about how Duffield nails the visual yuks, both kinds, in the first half (wild!) before laying into the grief and pain later on (quit laughing! it's not funny anymore!). "Spontaneous" allows Langford's Mara, blase swagger incarnate, and Plummer's stealth charmer enough unaffected sincerity to make it stick. Onto that sticky stuff, the script applies comforting reminders: Stuff happens. We don't know how long we have. Seize the day.

These are seful reminders in any calamitous time, but in metaphoric terms, even with good actors and a solid sense of craft, sometimes an exploding teen is just an exploding teen.

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'SPONTANEOUS'

Two and a half stars (out of four)

MPAA rating: R (for teen drug and alcohol use, language and bloody images throughout)

Running time: 1:37

Now streaming on Amazon Prime, Vudu and Fandango Now